I don't know him, but I use usually git while colleagues would rather use mercurial, bazaar or fossil. Basically, any distributed version control system. I prefer git because it has more features and I want to learn how to best use them. Before that I used fossil because it was simple and all data was stored in a single file (SQLite database), but some small annoyances and bug drove me off. Bazaar I used a bit after inheriting a project, but it lacked features to me, mostly easy branching. Mercurial I have never used.